The invention relates to a hydraulic prop for individual prop support in underground mining and tunnel construction, with a filling and drawing valve integrated in the prop head, whereby said filling and drawing valve has on the end side of its case a coupling piece for the setting gun with a gripping groove and locking shoulder and on the inside a return valve for setting, a non-return valve for drawing, and a pressure-limiting valve for securing the prop against overload, whereby the valve case of the pressure-limiting valve at the same time represents the piston for the non-return valve which has a seal shoulder which is formed in a corresponding manner with the seal seat at the inside case wall and whereby the pressure medium is removed in an environmentally harmless manner via a hose connection which may be clamped to the coupling piece.
Individual hydraulic props are used strategically in underground mining and in tunnel construction in order to secure cavities which were created by mining. For this purpose they are clamped between top wall and footwall or between floor and head. In addition, they are also used in the longwall in the transition area, where due to the daily progress in the mining they must then be moved one or several times a day. Their use is also mandatory in situations where due to rock conditions a shield-type support or a similar support cannot be used or can only be used with great difficulties. This applies also for semi-steep positioning. Especially if the hydraulic props must be moved daily, the pressure fluid, which consists of a water-oil mixture, in the past was sprayed into the environment during the drawing, thus causing the retraction of the hydraulic prop. Although the water-oil mixture contains only small amounts of oil, it cannot be avoided that the sprayed pressure fluid reaches the shaft bottom and is pumped from there to the surface, where it then automatically and inevitably causes environmental burdens. In addition, this process only permits a one-time use of the water-oil emulsion, i.e., it must be supplemented and replaced continuously with newly prepared pressure fluid.
Because of these problems, the water-in-oil emulsion released during the retraction of the hydraulic prop for some time has been collected, removed, and then reused in the pump. German DE-GM 89 12 529 describes for instance that the escape of the oil-containing fluid into the mine chamber can be prevented by pressing the pressure fluid via a hydraulically unlocked non-return valve from the same valve case end into the individual prop, and removing it again during the drawing. Thus the pressure medium flows into the return duct during drawing, whereby the drain process may be accelerated with a Venturi tube or similar devices, whereby the pressure fluid is then again used to set the prop. The disadvantage in these known hydraulic props and corresponding valves is the very complex construction of this multipurpose valve which otherwise is known from DE-OS 35 04 878. In order to be able to open the non-return valve, this already complex valve body has a bore which guides the pressure fluid to the rear of the valve case of the pressure-limiting valve, so that the latter is lifted from the valve seat when the non-return valve is loaded correspondingly. Either the pressure fluid must be added via a separate setting gun, or it must have been ensured or must be ensured in a different manner that the pressure fluid cannot flow off through this valve into the prop interior.